Self-tuning trajectory control of small body landing mission based on risk prediction

Aiming at the technical requirement of autonomous terrain obstacle avoidance during small body landing missions, a self-tuning control method of landing trajectory is designed. Firstly, according to the terrain height data of the small body surface measured by the lander's laser range finder (LRF), a terrain fitting curve can be obtained, then the terrain trend in the forward direction of the lander is estimated. After calculating the altitude difference between the lander and the estimated terrain,the probability of the lander colliding with terrain obstacles at the current moment is assessed. When the state of the lander no longer satisfies the relative altitude constraint, an autonomous obstacle avoidance mode is activated. An analytical guidance law with three adjustable thrust coefficients is derived for this mode, which is designed to able to control the geometric curvature of the landing trajectory in real time, since curvature is a crucial factor which influences the trajectory's obstacle avoidance performance. Based on the relationship between trajectory curvature and thrust coefficients, an adaptive module of the landing controller is designed. The module can calculate the desired curvature of the landing trajectory after comprehensively considering the obstacle avoidance requirement and the lander's thrust amplitude constraint, and obtain the values of thrust coefficients. The simulation results show that this adaptive trajectory curvature control method has better performance in obstacle avoidance than the analytical energy optimal guidance law commonly used in planetary landings.